WASHINGTON — House Republicans scouring for evidence of overreaching environmental regulations are taking aim at a two-decade-old, taxpayer-funded scientific study by Harvard researchers that linked air pollution to disease and death.

Even though the landmark study has held up under intense scientific scrutiny since its publication in 1993, the House Committee on Science, Space, and Technology took the rare step of issuing subpoenas last month demanding access to the study’s raw data about thousands of individual subjects.

The committee also subpoenaed raw data from a 1995 study of American Cancer Society health data on 1.2 million individuals that confirmed the findings of the earlier review, that air pollution is associated with higher rates of emergency room visits for asthma and other respiratory ailments, hospitalizations, and mortality.

Both studies — peer-reviewed and published in prestigious medical journals — have long been on the target list of some in the GOP because they have been repeatedly cited by the Environmental Protection Agency when it justifies the need for new regulations on power plant emissions and other air pollutants. The agency has estimated that tighter Clean Air Act rules adopted since 1990 saved 160,000 lives in 2010 and will save 230,000 lives in 2020.

The authors of both studies have resisted demands to open up their data to public scrutiny. In the case of the Harvard study, for instance, they cite the need to keep the identities and health status of some 8,000 study subjects in six communities, including Watertown, Mass., confidential. They contend that, even if names and addresses are removed, it would be possible for someone to determine the identities of many subjects based on their age, hometown, and date of death. The controversy poses a test for government officials and scientific researchers, who increasingly are being asked to balance the health care privacy rights of individuals against demands for data from outside researchers, the public, and, politically motivated critics.

Republicans argue that details of taxpayer-funded research, used to shape crucial public policy, should be available to the public.

“Regulations based on secret data have no place in a democracy,” said Representative Lamar Smith of Texas, chairman of the Committee on Science, Space, and Technology, in a statement to the Globe this week. “EPA is using the subpoenaed data to support regulations that could cost the American people billions of dollars.”

But as the political and legal tussle over the studies has escalated, Democrats and environmental advocates are calling the House subpoena an abuse of power. They say the demands for openness are part a broader effort by the GOP to fight regulations by attacking the underlying science on climate change and pollution.

“To the extent that that data is now going to be the target of politicking is unfortunate and the wrong way to go about policy-making,’’ said US Representative Joseph Kennedy III, the Massachusetts Democrat who is a member of the committee. The government provides financial backing to independent scientists and academic institutions to develop empirical evidence, he said, and “subjecting that to the political whims of the day sets an inappropriate precedent.”

The Harvard and American Cancer Society study authors have previously permitted outside reviews by researchers who pledged to keep the personal details confidential, including an exhaustive, multiyear analysis completed in 1997 that validated the results of both studies. That 1997 review — performed by the Health Effects Institute, a nonprofit corporation jointly funded by the EPA and the automobile industry — may have settled to the satisfaction of scientists the factual questions about links between pollution and human health. But it did not put the political controversy to rest.

The stakes in Washington have continued to rise with increased efforts by the Obama administration to curb the presence of greenhouse gases and other toxins, including ozone and mercury, in the atmosphere. In December, the EPA issued new, more stringent rules to reduce airborne particulates, which the agency estimates will cost industry $350 million a year in compliance costs, while saving $9 billion in annual health benefits. Those rules were opposed by industry groups, including the US Chamber of Commerce.

While Republicans say they want to dig through the studies to make sure they were performed appropriately, critics say they are hunting for fodder for further partisan attacks.

“Repeatedly kicking at these old studies has become a favorite tactic of those who resist regulation and try to sow doubt where there is very little legitimate, remaining scientific doubt about the big picture,”’ said Michael Gerrard, a professor at Columbia Law School and director of the Columbia Center for Climate Change Law.

The controversy over the air pollution research intensified during this year’s Senate confirmation battle over President Obama’s new EPA administrator, Gina McCarthy. After she was confirmed, Smith authored a Wall Street Journal op-ed column titled “The EPA’s Game of Secret Science,” which accused the EPA and McCarthy of stonewalling his requests for air pollution study data.

The House subpoena, the first issued by the Science and Technology Committee in 21 years, was approved on a party line vote Aug. 1. It was issued to the EPA, which commissioned both studies and, according to Republicans, has the legal authority to demand production of the materials from study leaders at Harvard and, in the case of the American Cancer Society study, the lead researchers at Brigham Young University.

The EPA missed an Aug. 19 deadline to produce the data, and the committee may pursue further action if the information is not submitted by the end of September. That could include a subpoena issued directly to Harvard.

“If EPA continues to default on its subpoena obligations, I will not hesitate to pursue all other means available to compel production of the relevant data,” Smith said in his statement to the Globe.

Harvard said it has complied with all requests it received from the EPA to provide information. “We will continue to provide all of the information that we possibly can while keeping in mind our confidentiality obligations to the research participants,’’ said Kevin Casey, Harvard’s associate vice president for public affairs. Violating those obligations, Casey added, would not only be an ethical breach, but could “significantly undermine” researchers’ ability to recruit participants for future studies.

Douglas Dockery, a prominent air pollution researcher at the Harvard School of Public Health who was lead author on the Harvard study, was not available for comment. His colleague on that paper, C. Arden Pope III, an economics professor at Brigham Young University who also was lead author on the American Cancer Society study, said there was no attempt to hide information from Congress or the public.

“Characterizing the ACS and Harvard Six-Cities studies as ‘secret science’ is a misrepresentation of the truth,’’ Pope said in remarks he e-mailed to the Globe.

“We have continued to be actively involved in open, collaborative, extended analysis efforts,’’ he added, “using the data and information in such a way that contributes to scientific understanding and that does not violate commitments to the privacy and confidentiality of research participants.’’